Our invention relates to a piston membrane pump.
A piston membrane pump is known comprising a piston and a membrane hermetically separating a feed chamber and a piston working chamber. The membrane is operated by the piston which oscillates back and forth in the piston working chamber, which is completely filled by a hydraulic medium. The piston membrane pump is also provided with a supply container for the hydraulic medium, which is connected to the piston working chamber by a refill valve. A moveable force-transmitting element is displacable against the force of a spring toward the end of a piston stroke producing a lowered pressure in the membrane working chamber. Displacement of the moveable force-transmitting element against the spring causes the opening of the refill valve.
This known piston membrane pump is also described in a technical report, "Controlled Membrane Pump for Large Throughput" of the applicant.
This type of piston membrane pump has heretofor been reliably operated for extended periods only when the membrane is made of plastic.
Plastic membranes have about an order of magnitude higher elasticity than steel membranes. Attempts up to now to make membrane pumps with freely oscillating steel membranes have failed, since steel membranes succumb to the load after a short time at their clamped portions or other locations. The Author, Vetter, of the Reference work "Pump", Vulkan-Press, Essen, 1987, p. 346, lower right column, reports that the use of metal membranes in freely oscillating membrane pump structures would never succeed.
For membrane pumps using freely oscillating plastic membranes one is limited to special application situations, pressures and mediums so that the plastic membrane can withstand the operating conditions.
In the membrane pumps known up to now with metal membranes the membrane works between cuplike curved, partially planar perforated bearing surfaces, which define the working chamber.
The perforated contacting surfaces of the described system lead to a series of disadvantages:
The metering of suspensions or contaminated media is not readily possible. Solid material clogs the clamped edge region between the membrane and the perforated plate and penetrates the membrane Also the membrane bears on the central portion of the perforated plate on overfilling of the hydraulic system produced by too low a draw pressure, for example with too long narrow low pressure lines, too high filtration or valve resistance, and with plugged members in the low pressure line.
The perforated plates are complicated to cast or mold and are an expensive component.
The perforated plates produce disadvantageous pressure losses so that viscous media can be fed only with the provided supply pressure.
On overfilling the membrane is pressed into the front perforated plate. Because the molding or casting of this plate results in a plate which does not exactly fit the form of the freely oscillating membrane, the membrane is deformed unsatisfactorily, which leads to a lifetime which has been shortened disadvantageously.
Finally, the principle of the double membrane pump is known, in which two membranes are separated from each other by a fluid filled chamber. The hydraulic-side membrane operates between cup-like boundary surfaces and takes control of the medium-side membrane, which has cuplike contacting surfaces only on the fluid filled chamber side, the medium side being free of them. The filled intermediate space provides however an additional dead space. The filling is expensive and the maintenance of an exactly filled volume is problematical.